Process for the distillation of ammonia



Oct. 15, 1935. D. PYZEL PROCESS FOR THE DISTILLATION OF AMMONIA OriginalFiled June 7, 1932 L 0; co: 6mg

L 0; vczoou lnvznTor= Dania] Pqzel 51 his Afiornaq Patented Oct. 15,1935 v UNITED STATES V l rnocsss ron THE msrmm'rion or AMMONIA I DanielPyzel,'Piedmont, Calii., assignor to Shell Development Company, SanFrancisco, alii., a corporation oi Delaware Original application June I,1932, Serial No.

Divided and this application May I,

1934, Serial No. 724,350. In Canada October 2 Claims.

This application is a division of my application, Serial No. 615,807filed in the U. S. Patent omce June "I, 1932.

In plants ior the production oi ammonia and its products which comprisean ammonia synthesis.

unit and various units using ammonia as a raw material, economicaloperation necessitates that suitable means for storing ammonia beprovided so I that, in case oi shut down oi either theammonia l0producing or ammonia utilizing units for necessary repairs orfluctuating consumption, et cetera,

' the remaining unit or units can operate ior a time without the aid ofthe other.

Some oi the more recent processes ior am- Iii monia synthesis producethe ammonia in the gaseous state. This ammonia gas could be stored asliquid anhydrous ammonia but this necessitates llqueiying the gas andstoring the resultant liquid anhydrous ammonia in pressure vessels. The

20 above method, however, is expensive and cumbersome. The ammonia gascould also be stored as a as but the space required would be too great.

The easiest method oi storing the ammonia gas is to absorb 'it in waterforming aqueous solution 25 of ammonia. This aqueous solution oi ammoniacan be stored in ordinary storage tanks. The gaseous ammonia can bereadily obtained again when required by distillation of the aqueoussolution oi ammonia.

30 It is a purpose of this invention to devise a process ior theproduction oi gaseous ammonia irom aqueous solution oi ammonia.

It is a further purpose oi this invention to provide a process andapparatus suitable ior the al- 35 ternative formation oi aqueoussolution oi ammonia irom pure ammonia and the formation oi gaseousammonia irom aqueous solution oi ammonia. 1

The iurt'her objects and advantages oi my in 40 vention will be moreiully understood irom the iollowing detailed description throughoutwhich reference is made to the accompanying drawing which shows atypical arrangement oi my apparatus. In this description it should beunder- 45 stood that although the terms "tower, bubble column" andstripper" are each used ior certain parts oi the apparatus, such use issolely ior the sake of cleamess of description as various types oitowers or columns can be used at these points. 50 In operating so as toform aqueous solution oi ammonia, ammonia gas is conducted into theapparatus through line I. This gas, aiter passing through a suitablecontrol valve 2, passes by way oi inverted U 3 into the lower portion01' tower 4. 55 Aqueous solution oi ammonia oi medium strength (iorexample concentrations oi irom 5% to 20% ammonia in water depending uponthe concentration desired in the final product) is sprayed into v thetop oi this tower from line I. The major part of the ammonia enteringthe tower is absorbed 5 by the medium strength aqueous solution oiammonia flowing down through the tower. The resulting strong aqueoussolution oi ammonia collects in the bottom oi the toiwer. a

The presence of non-condensible gases such as hydrogen, nitrogen, etcetera, inthe ammonia gas will prevent the complete absorption oiammonia in tower 4 The unabsorbed ammonia and noncondensible gases areled oii irom the top of tower 4 through pipe 6 and valves I into thelower portion oi a scrubber 8. The gas mixture passes up-' wardcountercm'rent to water sprayed into the, scrubber irom line 8controlled by. valve 30. The gases not absorbed are vented to theatmosphere through pipe Ill.

Strong aqueous solution oi ammonia collects in the bottom oi tower l andis withdrawn through pipe II and forced by means oi pump I! throughcooler ii. The cooled aqueous solution oi ammonia is passed into line Iand sprayed into the top oi tower l as above-mentioned. The diluteaqueous solution of ammonia collecting in the bot- 7 tom oi the scrubber8 also flows into line I i and is mixed with the strong aqueous solutionoi ammonia circulating stream.

In this manner the required quantity oi water ior absorption firstserves to scrub the outgoing non-condenslble gases and thereaiter takesup its full quota oi ammonia gas while flowing down through the tower lintermixed with the clrculating solution which serves to carry oi! theheat oi absorption. 3 Strong aqueous solution oi ammonia is-continually'withdrawn irom the bottom oi tower 4 through pipe It. The amount oiaqueous solution 40 oi ammonia withdrawn isregulated bymeans oi a floatvalve indicated at ii. The aqueous solution' oi ammonia drawn on! iscooled by being passed through heat exchanger It countercurrent tocooling water and is then run to storage through line H. 1

The concentration oi the aqueous solution oi ammonia produced isregulated by controlling the temperature in the bottom oi the tower 4.This temperature control is in turn effected. by regulating the rate oiflow oi the circulating stream which can be accomplished by valve 29. Itthe top oi tower 4 is kept as cool as possible it will prevent too largea quantity oi ammonia from being carried over into the scrubber I by thenon-condensible gases.-

When it is desired to obtain gaseous ammonia from aqueous solution ofammonia, the equipment is augmented by a bubble column I. by openingvalves I! and 20. The scrubber 8 is cut oil from the system by closingvalves I and 2 I, and opening valve 22. The process then operates asfollows:

The aqueous solution of ammonia is pumped from storage through line I"!into heat exchanger l6 where it is heated by being passed countercurrentto hot water leaving the bubble column The heated aqueous solution ofammonia passes into the upper portion 01 the bubble column I! while atthe same time steam is injected into the bottom of the bubble columnthrough line 23 controlled by a valve 24. The steam passing upwardthrough the column heats the aqua ammonia flowing downward causingammonia gas together with some water vapor to be driven off. Thisgas-vapor mixture flows from the bubble column through line 3| into thebottom section of tower 4.

The ammonia gas and water vapor passing upward through the tower 4 iscooled by a downward flowing stream of cold aqueous solution of ammonia.By this step the major part of the water vapor and some of the ammoniaare condensed so that the ammonia gas leaving tower 4 through line 6 andvalve 22 is substantially free from water vapor. The ammonia gas iscarried through pipe 25 to ammonia consuming units. The cooling in tower4 is accomplished by means of a rapidly circulating stream of aquaammonia which is withdrawn from the bottom of tower 4 pumped throughcooler l3 and sprayed into the top of the tower from pipe 5. Parts ofthe cooled aqueous solution of ammonia is led from line 5 into the topof bubble column l8 through hne 26 controlled by valve IS. 'The aqueoussolution. of

ammonia thus sprayed. into the bubble column serves as reflux material.I

The water entering the system as aqueous solution of ammonia, freed fromits contained ammonia gas in the bubble column I8, collects in thebottom of the column. 'This hot water is continually withdrawn throughline 21 and passed aomaaa the water collecting in the bottom of thecolumn at its boiling point.

One of the chief advantages of my invention is that the apparatusprovides a means for'either distillation or absorption processesutilizing a minimum of equipment.

Another advantage is that the system of indirect cooling by acirculating stream of aqueous solution of ammonia, when distillingserves to cool the ammonia gas, and to produce a condensate suitable forreflux. When absorbing, the circulating stream of aqueous solution ofammonia serves to remove the heat of reaction of the ammonia gas and thewater. My process is also particularly suitable for large scaleproduction or ammonia trom aqueous solution of ammonia or the reverseprocess.

The further advantages of my invention will be apparent to those skilledin the art.

I claim as my invention:

1. In a process for the preparation of gaseous ammonia from an aqueoussolution of ammonia the steps comprising contacting an aqueous solutionor ammonia with-steam in atower, withdrawing the ammonia gas and watervapor produced, passing said ammonia gas and water vapor in a secondtower countercurrent to a cold aqueous solution of ammonia having asubstantially limited capacity for the further adsorption of ammonia,withdrawing a hot aqueous solution of ammonia from the bottom of saidsecond tower, cool ing the same and injecting part of the cooled aqueoussolution of ammonia into the upper portion 01 said first tower, and partinto the upper portion of said second tower, while withdrawing gaseousammonia from the upper portion of the second tower.

v2. In a process for the preparation of gaseous ammonia from an aqueoussolution of ammonia the steps comprising-passing an aqueous solution 40of ammonia countercurrent to steam in a tower, withdrawing the ammoniagas and water vapor produced, passing said ammonia gas and water vaporcountercurrent to a cold aqueous solution of ammonia having asubstantially limited capacity for the further absorption of ammonia,withdrawing a hot aqueous solution of ammonia from the bottom of saidsecond tower, cooling the same, injecting part of the cooled aqueoussolution of ammonia into the upper portion of said first tower and partinto the upper portion of said second tower, withdrawing gaseous ammoniafrom the-upper portion of the second tower and withdrawing water fromthe bottom of the first tower.

' DANIEL PYZEL.

